The present invention relates to a method for manufacturing a liquid crystal display (hereinafter referred to as LCD) of an active matrix type with a thin film transistor (hereinafter referred to as TFT) used for a switching element, and more specifically to a method for manufacturing an active matrix type liquid crystal display using TFT (TFT-LCD) with improved display characteristics and productivity by forming a TFT array substrate with little point defect and line defect through five photo-lithography processes also using a line material having low resistance for a gate line and a source line.
Electro-optic elements for a display using a liquid crystal are popularly applied to products with its thin element and low electric consumption being highly appreciated, as one of the flat panel displays alternative to CRT.
For an electro-optic element for display using a liquid crystal, there are a simple matrix type LCD and TFT-LCD which uses TFT as a switching element. The TFT-LCD which has characteristics superior to CRT or the simple matrix type LCD in terms of portability and display quality has been popularly commercialized as notebook-size personal computers and the like. Generally, a liquid crystal layer is interposed between a TFT array substrate and an opposite substrate in TFT-LCD. On the TFT array substrate, TFT is formed as an array. On the opposite substrate, a common electrode and a color filter are mounted. On the outside of this kind of TFT array substrate and the opposite substrate, a polarizer is provided, respectively, and in addition, on one side, a back light is provided. With this kind of construction, satisfactory color display can be obtained.
However, in the TFT-LCD, it is necessary to fabricate the TFT array substrate in which TFT is formed as an array on a glass substrate using a technique for preparing semiconductor, and a great number of processes are required. As a result, there are problems that various defects are likely to occur, yield is decreased, more manufacturing equipment is required and that manufacturing cost is increased thereby.
As a method for solving these problems, Japanese Unexamined Patent Publication No. 268353/1998 discloses a method for manufacturing an active matrix type liquid crystal display, in which TFT array substrate is prepared through five photo-lithography processes.
FIGS. 7 to 9 are cross-sectional illustrations of a principal portion of a conventional TFT array substrate disclosed in Japanese Unexamined Patent Publication No. 268353/1998 (indicating components on an insulating substrate), and FIG. 3 is a plane explanatory view.
The cross-section of FIG. 7 schematically shows the cross-sectional construction taken on line Xxe2x80x94X of FIG. 3, while FIGS. 8 and 9 schematically show the cross sectional constructions of a TCP terminal portion provided outside the display area, respectively. The TCP connects a signal potential source for supplying signal potential to be inputted to a gate line, a source line, an auxiliary capacity line and a common electrode of the opposite substrate, with the gate line, the source line, the auxiliary capacity line and the common electrode.
Referring to FIGS. 7 to 9 and FIG. 3, numeral 1 denotes a gate electrode, 2 an auxiliary capacity electrode, 3 a gate insulating film, 4 a semiconductor active film, 5 an ohmic contact film, 6 a drain electrode, 7 a source electrode, 8 a passivation film, 9 a pixel contact hole, 10 a portion having auxiliary capacity (hereinafter referred to as xe2x80x9cauxiliary capacityxe2x80x9d), 11 an pixel electrode, 12 a first display portion lead-out line, 13 a first TCP connection electrode, 14 a first TCP terminal contact, 15 a first TCP connection range, 16 a second display portion lead-out line, 17 a second TCP connection electrode, 18 a second TCP terminal contact, 19 a second TCP connection range, 20 an auxiliary capacity line, 21 a gate line, 22 a source line and 23 a semiconductor active film and ohmic contact film.
The gate electrode 1 is an electrode which is a part of the gate line 21 or an electrode serving as a terminal which branches off from the gate line 21 to connect to each TFT. The auxiliary capacity electrode 2 is an electrode which branches off from the auxiliary capacity line 20 and part of which is extended to a position where the electrode overlaps the pixel electrode 11. Between the auxiliary capacity electrode 2 and the pixel electrode 11, the auxiliary capacity 10 is formed with a laminated film comprising a first insulating film (the gate insulating film 3) and a second insulating film as a dielectric substance. The auxiliary capacity 10 is formed in electrically parallel to a liquid crystal capacity formed between the pixel electrode 11 and the common electrode via a liquid crystal. The semiconductor active film and ohmic contact film numbered as 23 in FIG. 3 comprises two, upper and lower layers which are numbered as 4 and 5 in FIG. 7.
This conventional technique discloses a method for manufacturing a TFT array substrate through five photo-lithography processes. As an effect, it is stated that since there is no case where the source line 22 and the source electrode 7 cross over the difference formed by the semiconductor active film and the ohmic contact film 23 within the display area, disconnection of the source line 22 and the source electrode 7 can be substantially eliminated. It is also stated that though the semiconductor active film with ohmic contact film 23 is left around the pixel electrode 11, by constructing the pixel electrode, and each of the semiconductor active film with ohmic contact film 23, and the source line 22 to be separated via the second insulating film (the passivation film 8), it is possible to reduce a simple short-circuit between the source line 22 and the pixel electrode 11 due to inferior patterning of the semiconductor active film with ohmic contact film 23 and the source line 22 or a short-circuit caused by a resistance reduction of the semiconductor active film 4 due to a light irradiation.
However, according to a conventional technique disclosed in Japanese Unexamined Patent Publication No. 268353/1998,in case of using a low resistance line material (such as Al) for a metal thin film material of the gate line 21 and the source line 22, an oxide layer will be formed between the part comprising the gate line 21 or the source line 22, and the pixel electrode 11 electrically connected therewith. The oxide layer causes high contact resistance at each of the contact part of the gate line 21, and the pixel electrode 11 or the contact part of the source line 22, and the pixel electrode 11. There arises a display defect. That is, it was impossible to prepare TFT-LCD by using a low resistance line material such as Al for a line material according to the above method.
The present invention relates to a method for manufacturing electro-optic elements including a first insulating substrate wherein a display pixel having a pixel electrode in which a TFT is electrically connected is formed as an array, a TFT array substrate wherein a gate line for sequentially scanning each TFT intersects at right angles a source line which provides a signal potential to the pixel electrode and a second insulating substrate having an opposite substrate on which a color filter and a common electrode are formed, wherein the TFT array substrate and the opposite substrate are affixed with a liquid crystal layer interposed in-between and polarizers are placed outside the TFT array substrate and the opposite substrate, respectively, comprising the steps:
(a) forming the above gate line and the gate electrodes of the TFT by patterning a first metal thin film by a first photolithography process after forming the first metal thin film on the first insulating substrate;
(b) patterning by dry etching a semiconductor active film and an ohmic contact film by a second photolithography process wherein the semiconductor active film and the ohmic film are formed in a continuous shape and are larger than a portion in which the source line and the TFT are formed, wherein said patterning step occurs after forming a first insulating film, the semiconductor active film, and the ohmic contact film;
(c) patterning a second metal thin film by a third photolithography process after forming the second metal thin film to form a source line as well as a source electrode and a drain electrode of the TFT and etch-removing by dry etching the ohmic contact film protruding from the source line, the source electrode, and the drain electrode;
(d) patterning a second insulating film and the first insulating film in a fourth photolithography process after forming the second insulating film and forming a pixel contact hole that penetrates at least to the drain electrode surface, a first contact hole that penetrates to the first metal thin film surface, and a second contact hole that penetrates the second metal thin film surface; and
(e) patterning a conductive thin film and forming the pixel electrode by a fifth photolithography process after forming the conductive thin film.
The first method for manufacturing the electro-optic device of the present invention further comprises at least two layers having a first layer of the above first metal thin film comprising metal and a second layer thereon obtained by adding nitrogen atoms on a metal.
The second method for manufacturing the electro-optic device of the present invention further comprises at least two layers having a first layer of the above second metal thin film comprising metal and a second layer thereon obtained by adding nitrogen atoms on a metal.
The third method for manufacturing the electro-optic device of the present invention further comprises the above first and second metal thin films each having at least two layers of a first layer comprising metal and a second layer thereon obtained by adding nitrogen atoms on a metal.
The forth, fifth and sixth method for manufacturing the electro-optic device of the present invention is that in the first, second or third method, the above pixel electrode can be formed by a non-crystallized, transparent thin conductive film.
The seventh, eighth and ninth method for manufacturing the electro-optic device of the present invention is that in the first, second or third method, the above non-crystallized transparent thin conductive film is multi-crystallized by annealing after the arraying step of the TFT array substrate prepared according to the above method with properties of the TFT array substrate prepared according to the above process being stabilized.
The tenth method for manufacturing the electro-optic device of the present invention is that in the first method, the second layer which is obtained by adding nitrogen atoms to the above metal can be positioned in the vicinity of the interface of the above first metal thin film electrically connected to the transparent, thin conductive film which forms the above pixel electrode through the above first contact hole.
The eleventh method for manufacturing the electro-optic device of the present invention is that in the second method, the second layer which is obtained by adding nitrogen atoms to the above metal can be positioned in the vicinity of the interface of the above second thin metal film electrically connected to the transparent, thin conductive film which forms the above pixel electrode through the above second contact hole.
The twelfth method for manufacturing the electro-optic device of the present invention is that in the third method, the second layer which is obtained by adding nitrogen atoms to the above metal can be positioned in the vicinity of the interface of the above first and second thin metal films electrically connected to the transparent, thin conductive film which forms the above pixel electrode through the above first or second contact hole.
The thirteenth, fourteenth and fifteenth method for manufacturing the electro-optic device of the present invention is that in the first, second and third method, the material comprising the above first and second metal thin film can be one metal selected from the group consisting of Al, Ta, W, Cu and Ag or an alloy comprising at least one of these metals as a main component.
The sixteenth, seventeenth and eighteenth method for manufacturing the electro-optic device of the present invention is that in the first, second and third method, the non-crystallized transparent, conductive thin film for the above pixel electrode can comprise one selected from the group consisting of In2O3, SnO2, ZnO, an oxide obtained by mixing In2O3 with SnO2 and an oxide obtained by mixing In2O3 with ZnO.